Shape templated synthesis

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

The advantage of template synthesis is that organo or hydrogelator templates can direct the shape-controlled synthesis of oxide nanotubes. Recent reports describe the use of carbon nanofibers as a template for the shape-controlled synthesis of zirconia, alumina and silica nanotubes [78]. The shape of vapor grown carbon nanofiber... 

Ogihara H, Sadakane M, Nodasaka Y, Ueda W (2006) Shape-controlled synthesis of Zr02, AI2O3 and Si02 nanotubes using carbon nanofibers as templates. Cbem Mater 21 4981-4983... 

Jana, N. R., Gearheart, L. Murphy, C. J. Seed-mediated growth approach for shape-controlled synthesis of spheroidal and rod-like gold nanoparticles using a surfactant template. Adv. Mater. (Weinheim, Ger.) 13, 1389-1393 (2001). 

Foss, C.A. Jr, Hornyak, G.L., Stochkert, J.A. and Martin, C.R. (1994) Template-synthesis nanoscopic gold particles optical spectra and the effects of particle size and shape. J. Phys. Chem., 98, 2963-2971. 

The surfactant templated synthesis of mesoporous ceramics was first reported in 1992 [1], and since that time there has been a veritable explosion in the number of papers in the area. There has been particular interest in the functionalization of mesoporous ceramics [2-S]. As outlined in Figure 1, the original synthesis employed rod-shaped micelles composed of cationic surfactant molecules as the pore template (more recently, this methodology has been extended to a wide variety of other surfactant systems and reaction conditions). When exposed to routine sol-gel conditions, the cationic micelles undergo an anionic metathesis with silicate anions, resulting in a glass-coated log which... 

Hard-tcmplatc synthesis can provide micro- and nanocontainers with a controlled geometric shape. However, this approach requires complicated synthetic steps, including the dissolution of the template in corrosive media. Collapse of the hollow structure after template removal is also a critical problem. Therefore, the potential drawback of using hard templates forced scientists to search for more efficient and facile routes to prepare CPCs. Among these newly developed approaches, the soft-template method is considered a powerful tool as an alternative strategy to hard-template synthesis. 

Diamond-Shaped CNTs Using Template Synthesis.545... 

Xu, R, Wharton, J.E., Martin, C.R. Template synthesis of carbon nanotubes with diamond-shaped cross sections. Small 3, 1718-1722, 2007. 

Fujikawa D, Uota M, Sakai G, Kijima T (2007) Shape-controlled synthesis of nanocarbons from resorcinol-formaldehyde nanopolymers using surfactant-templated vesicular assemblies. Carbon 45 1289-1295... 

Templated synthesis assumes a direct correlation between shape and size of a SDA and of the surrounding cage. Whereas such direct action is only observed exceptionally [144], the use of a triquat molecule with D3h symmetry... 

Figure 19 Template synthesis of a [2]catenane. The U-shaped fragment contains a bidentate coordinating moiety, and the black dot represents a tetrahedrally coordinating metal ion. (Reproduced from Ref. 56. Springer, 1993.)...

My research group has been exploring a method for preparing nanomaterials called template synthesis. (For recent reviews see Refs. 1 and 2.) This method entails synthesizing the desired material within the pores of a nanoporous membrane or other solid. The membranes employed have cylindrical pores of uniform diameter (Fig. 16.1). In essence, we view each of these pores as a beaker in which a piece of the desired material is synthesized. Because of the cylindrical shape of these pores a nanocylinder of the desired material is obtained in each pore (Fig. 16.2). Depending on the material and the chemistry of the pore wall, this nanocylinder may be solid (a fibril) or hollow (a tubule). 

---